TY - JOUR
T1 - Conductance mutations of the nicotinic acetylcholine receptor do not act by a simple electrostatic mechanism
AU - Kienker, P.
AU - Tomaselli, G.
AU - Jurman, M.
AU - Yellen, G.
N1 - Funding Information:
We thank Dr. James B. Matthew for his comments, and Dr. James D. Lear for countless discussions. This research was supported by the Howard Hughes Medical Institute, by National Institutes of Health Grant K08 HL02421-02 (G. T.), and by Grant 3243 of the Council for Tobacco Research (G. Y.). Dr. Tomaselli is an Eli Lilly Clinician-Scientist of the Johns Hopkins School of Medicine.
PY - 1994
Y1 - 1994
N2 - Fixed negative charges in many cation channels raise the single-channel conductance, apparently by an electrostatic mechanism: their effects are accentuated in solutions of low ionic strength and attenuated at high ionic strength. The charges of specific amino acids near the ends of the proposed pore-lining M2 segment of the nicotinic acetylcholine receptor, termed the extracellular and cytoplasmic rings, have recently been shown to influence the single-channel K+ conductance (Imoto, K., C. Busch, B. Sakmann, M. Mishina, T. Konno, J. Nakai, H. Bujo, Y. Mori, K. Fukuda and S. Numa. 1988. Nature 335:645–648). We examined whether these charges might act by a direct electrostatic effect on the energy of ions in the pore, rather than indirectly by inducing a structural change. To this end, we measured the conductances of charge mutants over a range of K+ concentrations (ionic strengths). As expected, we found that negative charge mutations raise the conductance, and positive charge mutations lower it. The effects of cytoplasmic-ring mutations are accentuated at low ionic strength, but they are not completely attenuated at high ionic strength. The effects of extracellular-ring mutations are independent of ionic strength. These results are inconsistent with the simplest electrostatic model. We suggest a modified model that qualitatively accounts for the data.
AB - Fixed negative charges in many cation channels raise the single-channel conductance, apparently by an electrostatic mechanism: their effects are accentuated in solutions of low ionic strength and attenuated at high ionic strength. The charges of specific amino acids near the ends of the proposed pore-lining M2 segment of the nicotinic acetylcholine receptor, termed the extracellular and cytoplasmic rings, have recently been shown to influence the single-channel K+ conductance (Imoto, K., C. Busch, B. Sakmann, M. Mishina, T. Konno, J. Nakai, H. Bujo, Y. Mori, K. Fukuda and S. Numa. 1988. Nature 335:645–648). We examined whether these charges might act by a direct electrostatic effect on the energy of ions in the pore, rather than indirectly by inducing a structural change. To this end, we measured the conductances of charge mutants over a range of K+ concentrations (ionic strengths). As expected, we found that negative charge mutations raise the conductance, and positive charge mutations lower it. The effects of cytoplasmic-ring mutations are accentuated at low ionic strength, but they are not completely attenuated at high ionic strength. The effects of extracellular-ring mutations are independent of ionic strength. These results are inconsistent with the simplest electrostatic model. We suggest a modified model that qualitatively accounts for the data.
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U2 - 10.1016/S0006-3495(94)80781-7
DO - 10.1016/S0006-3495(94)80781-7
M3 - Article
C2 - 8161686
AN - SCOPUS:0028118783
SN - 0006-3495
VL - 66
SP - 325
EP - 334
JO - Biophysical Journal
JF - Biophysical Journal
IS - 2
ER -